Wood preservation process



United States Patent 3,464,782 WOOD PRESERVATION PROCESS Jacques L. Ricard and Robert D. Graham, Corvallis, and

John S. Mothershead, Albany, reg., assignors to Research Corporation, New York, N.Y., a corporation of New York No Drawing. Filed June 29, 1967, Ser. No. 649,796 Int. Cl. A01r 11/00; B27k 5/00; A611 1/00 U.S. Cl. 21-7 7 Claims ABSTRACT OF THE DISCLOSURE A method for controlling fungus-induced deterioration of wood wherein the wood to be protected is treated with ammonia and a halogen-containing fumigant.

This invention relates to a method for the preservation of wood and of products made from wood. In one specific aspect, the invention relates to the control of fungusinduced deterioration in wood.

Wood products are often exposed to conditions conducive to fungus-induced deterioration. The deterioration may be internal and occur even after external treatment with conventional water-borne or oil-borne preservatives.

We have discovered a new method for the protection of wood from fungusdnduced deterioration. According to the method of the present invention, the wood product to be protected is treated with ammonia and a halogen-containing fumigant which permeate the wood and destroy any fungi present and then interact Within the wood to produce substances having residual fungicidal activity.

It is, therefore, a principal object of the present invention to provide a method for the protection of wood from fungus-induced deterioration.

It is a further object of the invention to provide a method wherein the treating agent permeates the wood to be protected.

It is yet another object of the present invention to provide a method wherein the treating agent has both a fumigant effect and residual fungicidal activity.

More specifically, our invention is a method for controlling the fungus-induced deterioration of wood which comprises treating the wood to be protected with ammonia and a halogen-containing fumigant.

A fumigant is a gas, or a solid or liquid capable of ready volatilization under the conditions of use. Halogencontaining fumigants are well known to those skilled in the art. A list of such fumigants would include but not be limited to halogenated hydrocarbon fumigants such as ethylene dichloride, trichloroethylene, methyl bromide and the like, and inorganic halides such as sulfuryl fluoride. The list of halogens would include fluorine, bromine, iodine and chlorine.

Ammonia is employed in conjunction with the halogencontaining fumigant because of its toxicity to basidiomycetes and its ability to readily permeate wood. Ammonia also causes swelling of the Wood thereby increasing the rate of diffusion of the fumigant. The ammonia and the fumigant supplement each others toxic effects on the microorganisms present and chemically interact to form compounds such as primary, secondary, tertiary and quaternary amines and ammonium salts as well as ammonium halide salts having residual fungicidal activity.

It is apparent from the above that volatile loweralkylamines such as methylamine, ethylamine, isopropylamine, dimethylamine and the like may be used in place of ammonia. However, ammonia is preferred because of its high rate of diffusion through wood as well as its lower cost.

In the practice of the present invention, the wood to be protected is exposed concurrently or in alternate sequence 3,464,782 Patented Sept. 2, 1969 ice to ammonia and the halogen-containing fumigant. The exposure is by diffusion from the surface of the wood with the product to be protected enclosed in a sealed vessel or under gas-proof cover. In a less preferred embodiment, the treating agents may be sealed within the wood under conditions permitting the diffusion of their vapors through out the wood.

The multi-gas diffusion treatment of the present invention may be applied to wood products prior to use with or without further treatment with conventional preservatives. The treatment may also be employed to protect wood products in service, i.e., structural timbers and utility poles, or with wood products that have been removed from use but which are being reconditioned for resuse.

The multi-gas diffusion treatment of the present invention is further illustrated by means of the following nonlimiting examples using Douglas fir wood as the wood being protected against fungus-induced deterioration. Douglas firs and other conifers are used extensively as utility poles because of their low cost and desirable mechanical properties. Even though the poles are treated with liquidborne preservatives, they are still subject in use to heartwood or other deterioration caused by fungi of the genera Poria, Fomes, Polyporus, et cetera. Internal infection by such fungi cannot be detected in its earlier stages by visual inspection of the poles exterior but is established by culturing a wood core sample bored from the pole on a suitable growth medium.

Six Douglas fir poles in the early stages of decay and infected with viable Poria carbonica were placed in a metal tank equipped with an electric heater and blower. The tank was covered and made gas tight by means of a polyethylene tarpaulin. A total of four pounds of methyl bromide and eight pounds of anhydrous ammonia were supplied to the treating tank in alternating several pound portions. The temperature at the end of the 60 hour overall treatment was 47 C. No live organisms were recovered from the poles upon completion of the treatment or on further testing six months after treatment. The test for viable microorganisms involved culturing cores aseptically removed from the pore on malt extract agar.

Utility poles out of service were reconditioned by multi-gas diffusion followed by treatment with a conventional preservative solution. Using the system of the previous example, the gases were released gradually and alternately until a total of 1 pound methyl bromide and 0.3 pound ammonia were provided for each pole being processed. For best results, the methyl bromide should be introduced as a gas.

The poles remained covered for 24 hours after addition of the gases was complete, and the plastic sheet was removed. Subsequently, the poles were dipped in pentachlorophenol solution and reinstalled in service.

Sections of untreated green pole stock, 2 feet long and 9 inches in diameter, were placed in a retort. Steam was fed to the retort until a temperature of 250 F. (15 p.s.i.) was reached in the retort. After 48 hours of continuous exposure to steam the pole sections were removed from the retort and the ends packed with insulation material to prevent longitudinal heat loss. The insulated pole sections were then placed in a horizontal metal gas chamber made from a ZO-gallon drum, air was partially evacuated down to a pressure of 6 p.s.i. below atmospheric. Methyl bromide was introduced until the pressure rose to 5 p.s.i. below atmospheric, followed by ammonia to return the chamber to atmospheric pressure. The system was allowed to stand for 24 hours at 70 F.

No ammonium bromide salts were found on the surfaces of the pole sections except where the sections had touched the hot metal wall of the treating chamber. Wood core samples taken from the poles showed the presence of bromine by the Beilstein flame test and by the silver nitrate precipitation test. Ammonia was found in core samples taken one year after treatment in more than 90 percent of the samples tested.

The standard static bending test (ASTM 1965) was used to evaluate the eflect of methyl bromide and ammonia, singly and mixed, on wood strength in 1 by 1 by 16-inch specimens at 12 percent moisture content. The modulus of rupture (R) was calculated as follows:

3 Pl -s n where:

P=breaking load in pounds l=length of specimen in inches b=|breadth or width in inches h=height in inches.

The table which follows summarizes the data obtained with Douglas fir beams 1 by 1 by 16 inches in size in static bending tests. The modulus of rupture listed in the Wood Handbook (U.S. Forest Product Laboratories 1955) for coast-type Douglas fir at 12 percent moisture content is 1225x None of the test averages obtained exceeds the 16 percent coefficient of variation indicated in the handbook for the modulus of rupture. Hence, no significant etfect on strength can be attributed to gas treatment.

MODULUS OF RUPTURE, P.S.I.) 10

Treatment N113 and None NH; CH3Br CHsBr Average 12. 46 11. 99 11. 89 12. 19

Further experiments have shown, that under the conditions tested, a saturation equilibrium is reached inside and outside a pole when approximately 50 pounds of methyl bromide and 48 pounds of ammonia are employed per 1,000 cubic feet of wood. However, a lower proportion of ammonia can be used and still obtain a residual fungicidal effect. The preferred dosage for a pole 10 inches in diameter and 50 feet long would be 1.5 pounds methyl bromide and 0.4 pound ammonia. Under these conditions there would be formed 1.34 pounds of residual salts, about 0.15 percent based on weight of the wood. For in-service treatment, 1 pound of methyl bromide and 0.3 pound of ammonia would yield a salt concentration of 1.24 percent, based on weight of the wood, which would be ample for residual control of deteriorationcausing fungi.

In order to promote formation of salts in the wood and to lessen losses by deposition of salts on exposed surfaces, the interior of the wood undergoing treatment should be warmer than the surrounding environment. This diiference in temperature can be achieved with poles in service by treating them in early morning during the summer or by dielectric heating.

In another series of experiments, standard water saturated Douglas-fir stakes 94 x x 18 inches long were treated in a 20-gallon tank. After the tank was charged with the stakes and sealed, the pressure in the tank was reduced to 8.7 p.s.i. The tank was brought back to atmospheric pressure by rapidly releasing sulfuryl fluoride (B.P. -55 C.) into the tank. The pressure within the tank then decreased as the gas was absorbed into the wood. After the pressure had stopped dropping, it was again brought back to atmospheric this time by releasing ammonia gas into the tank. The cycle was repeated in several experiments. The stakes were removed from the tank and allowed to air dry. The treatment produced ammonia fluoride, a wood preservative and fire retardant, within the wood. The dry treated stakes were waterproofed by dipping in a rubber-based coating compound prior to use in soil.

Other variations falling within the scope of the present invention will suggest themselves to those skilled in the art. Our invention is as claimed.

1. A method for controlling the fungus-induced deterioration of wood which comprises contacting the wood to be protected with gaseous ammonia and fumigant consisting essentially of a halogenated hydrocarbon, said fumigant being reactive with ammonia to form within the wood a compound having residual fungicidal activity.

2. A method according to claim 1 wherein the ammonia and the fumigant are employed concurrently.

3. A method according to claim 1 wherein the ammonia and the fumigant are employed alternately.

4. A method according to claim 1 wherein the temperature of the wood being protected is higher than that of the surrounding environment.

5. A method according to claim 1 wherein the fumigant is methyl bromide.

6. A method for controlling the fungus-induced deterioration of wood which comprises contacting the wood to be protected with gaseous ammonia and a halogen-containing fumigant consisting essentially of a sulfuryl halide, said sulfu-ryl halide being reactive with ammonia to form within the wood a compound having residual fungicidal activity.

7. A method according to claim 6 wherein said sulfuryl halide is sulfuryl fluoride.

References Cited UNITED STATES PATENTS 939,015 11/1909 Hall 117-l08 1,210,491 1/ 1917 Kleinstuck 117-108 2,324,471 7/ 1943 Allen et a1 424350 XR 2,772,200 11/1956 Zakheim 424-162 XR 2,875,127 2/1959 Kenaga 424151 2,908,607 10/1959 Hager 424166 XR 3,092,537 6/ 1963 Brandts l17l08 XR 3,160,515 12/1964 Goldstein et a1 117-621 3,269,899 8/ 1966 Parker 424151 3,345,258 10/ 1967 Sidles 424350 XR FOREIGN PATENTS 24,967 2/ 1930 Australia.

MORRIS O. WOLK, Primary Examiner B. S. RICHMAN, Assistant Examiner U.S. Cl. X.R. 

